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BY BECKY LONG
The Pacific Northwest's temperate moist climate and frequent overcast days make it a slug and snail paradise. In Eugene, Oregon, the ubiquitous gastropod has become part of an annual celebration; a parade features a 40-foot slug and residents compete for the honor of being selected «Slug Queen.» Despite this tongue in cheek celebration of the slug, common responses to slugs and snails range from gastronomic delight to outright loathing. An assortment of least-toxic strategies can bring your slug and snail population under control.
Slugs and snails are mollusks, relatives of dams and oysters, not insects. There are several hundred species of snails and approximately 40 species of slugs in the United States. They come in a variety of sizes and colors and eat a wide assortment of plants. Introduced species have developed into serious pests whereas most native species tend to do little damage.
Both slugs and snails travel by secreting a mucus or slime on which they glide. This slime trail serves as a calling card, clearly identifying their presence in the garden.
Slugs and snails are hermaphrodites, having both male and female sex organs. Eggs are laid in masses of up to 100 eggs in soil, under debris,`rocks and plants. The eggs are large, 1/8 to 1/4 inch in diameter, and white or colorless.2 3 "A single slug can lay up to 400 eggs in a year, and they start doing it at the age of three months."3 Eggs will not hatch until they come in contact with moisture. Slugs may live up to 2 years and the common brown garden snail may grace your garden for up to 12 years.2
Moisture is the key to slug and snail survival. They avoid the sun, spending daylight hours hiding in cool, damp places such as under mulches, low-lying plant, boards, and in the soil. At night or on cloudy days, the migration begins.
Use an assortment of the following least-toxic control strategies and you should be able to keep your slug and snail populations at a tolerable level. Remember, complete eradication is not a realistic goal.
Reduce Habitat: Reduce attractive slug and snail habitat by removing unnecessary debris such as bricks, boards, garden clippings, and weeds in the vicinity of your garden. Mulching provides an ideal slug habitat so mulch lightly around plants that are attractive to slugs. Another option is to use mulches that are slug irritants such as shredded bark, crushed rock, or cinders. l ,4
Certain ground covers provide shady moist havens during the day. Ivy and other succulent groundcovers are favorite snail hangouts. Thinning out groundcovers increases sunlight and airflow, making the habitat warmer, drier, and less popular with slugs and snails.5
When possible, select plants that are not attractive to slugs and snails. Transplants can be kept indoors until they are big enough to resist slug and snail damage. Place plants attractive to slugs and snails away from groundcovers, grassy areas and other places where slugs might hide.3
Encourage predators: Snail and slug predators include snakes, toads, frogs, birds, beetles, fireflies and predatory snails. Some small farmers effectively use dud~s and geese to keep populations down. The large, black iridescent beetles you see in your yard are predators. Firefly larvae prey on slugs and snails with estimates that one larvae can eat 40 to 60 snails during its development
The decollate snail is the only predatory snail commercially available and its availability is restricted to Southern California for fear that' it will become a pest. It is found across the southern United States and along the eastern seaboard as far north as Pennsylvania. The decollate snail provides good control of the brown garden snail, but has much less interest in devouring slugs. Decollate snails move at a snail's pace, avoiding sunny areas. They dislike crossing concrete so they do not easily spread from block to block.
Humans are another predator. Those brown garden snails were originally brought over from France to be cultivated and prepared as escargot.
Rototill: Rototilling thoroughly can reduce slug populations. The tilling apparently kills the slugs as well as reducing the crevices in the soil where slugs hide.
Handpick: Handpicking serves as both a monitoring and a reduction strategy when used in combination with other control strategies. Handpicking can reduce snail populations, but slug populations may not be as effectively controlled. One study calculated that there were 6000 slugs in a large garden, and that for every slug collected in a night, there were 20 more still hiding.~
Handpicking is most effective on moist nights. Water lightly in the late afternoon to bring slugs and snails out of hiding.
A flashlight, a container, and a scooping utensil are essential tools. Recommended utensils include bare or gloved hands, tweezers, tongs, and a fork taped to the end of a stick. Use whatever works best for you.
Look for slugs and snails under plant leaves especially when a plant is drooping under an unknown weight. Look under boards, bricks, rocks, plant clippings, flower pots, garbage cans or other hiding places. You can kill your captives by squashing them. If that is unappealing, put captured slugs and snails in a container filled with soapy water to kill them. Flush captive slugs (not snails) down the toilet or drain the liquid from the jar and dump the contents in the trash.
Vacuum: Vacuuming is a more hands-off approach to removing slugs and snails. You'll have to refine your vacuuming techniques by trial and error. Use a water vacuum or one with a disposable bag.
Trap: Simple slug and snail traps can be made by placing boards, asphalt shingles,. old towels, rocks, plastic bags, or overturned flower pots on grass or soil surfaces. One foot square boards placed on one-inch risers are excellent snail havens. Asphalt shingles with the rough side up are good traps for slugs in grassy areas. These simple traps serve as easily identifiable locations that can be handpicked during the day. Traps also serve as a good tool for monitoring your slug and snail populations.3
Baits reputed to be attractive to slugs and snails may be used in traps. Baits include banana peels, inverted grapefruit halves, raw potato slices, lettuce leaves, dead slugs and snails, fermented bread dough or beer. Slugs are attracted to the smell of the yeast in beer. Colorado State University researchers conducted studies to identify the most popular brew and found that slugs preferred Kingsbury Malt Beverage, a nonalcoholic beer.4
Traps using beer as bait can be purchased commercially or you can make one yourself by placing a plastic container with a lid (such as a margarine container) into the ground, leaving 3/4 to 1 inch above ground. Cut entry holes into the container above ground level. (See drawing, below.) Slugs like fresh beer so replenish the trap frequently. You can make your own bait by mixing 1 cup water, 1 teaspoon sugar and 1/4 teaspoon yeast, and save the beer for yourself.4
Use Barriers: Wood ashes, diatomaceous earth, cedar wood chips, cinders, and copper strips or screening can ail be effective barriers against snails. Wood ashes and diatomaceous earth are only effective when dry. Cinders remain effective when wet. Salt does kill slugs and snails but repeated use can make the soil toxic to plants.
Copper barriers are effective against both slugs and snails. Slug and snail slime apparently interacts with the copper to produce an electric shock. Copper was more than 95 percent effective when the top edge of the strip was bent down to form a flange.
Copper strips or screening can easily be attached to raised wooden beds. Copper screening can also be buried in the ground at least four inches deep with two inches protruding above the soil.6 The top should be bent over forming a flange. (See the drawing at the bottom of the page for details.) Clearing the area adjacent to the copper barrier of all vegetation will prevent inadvertent vegetation bridges over the barrier. Copper barriers also keep resident population inside the barrier. So you'll want to concentrate regular handpicking efforts on the protected bed Finally, copper strips and screening can have sharp edges, so use them carefully.
Stay Away from Poisonous Slug Baits
Poisonous baits are hazardous to children, dogs, cats, birds, and other animals that ingest the bait.~ In addition, slug and snail populations can become "bait-resistant."5 According to Dr. Doreen Hock, head veterinarian of an emergency animal hospital, "Slug bait poisoning has to be one of the most hideous things we see. No pet owner would use it if they saw just one dog who'd eaten it."7
Least-toxic strategies for controlling slug and snail populations do work. By using several of these techniques, you can protect your plants from excessive slug and snail damage without exposing yourself, your children or your pets to toxic pesticides. .
1. Grossman, J. and H. Olkowski. 1990. Stopping slugs and snails. Common Sense Pest Control 6(1): 7-18.
2. Bio-lntegral Resource Center. Undated. Slugs and snails. Berkeley, CA.
3. Dickey, P. 1993. The baiting game: Meeting slimy pests in the garden. Alternatives. (Fall): 6-7.
4. Verbena, M., and J. Yates. 1991. 32 success secrets of super slug slayers. Organic Gardening. (April): 44-48.
5. Olkowski, W., S. Daar, and H. Olkowski. 1991. Common-sense pest control: Least-toxic solutions for your home, garden, pets and community. Newtown, CT: Taunton Press.
6. Hansen, Michael. Pest control for home and garden: The safest and most effective methods for you and the environment. 1993. Yonkers, NY: Consumers Union of United States Inc.
7. James, J. 1995. Slug wars: Safe ways to control the slimy pests. The Eugene Register Guard. (February 12.)
" Coping with slugs and snails ", J. of Pesticide Reform, Vol. 16, No. 1, pp. 22-23
Copyright © 1996 Northwest Coalition for Alternatives to Pesticides.
Reprinted with permission.
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